This invention relates to acoustic wave electromagnetic transduction, and in particular to electromagnetic ultrasound transducers suitable for nondestructive testing applications.
Surface acoustic wave electromagnetic transducers (EMT's) which do not require contact with conducting materials for acoustic transduction, are being used particularly in applications for nondestructive testing and measurement of the physical properties of materials. The utility of these transducers has been somewhat restricted, however, by limitations of present fabrication techniques and by the lack of adequate information about their properties and spectral characteristics for design purposes.
Until quite recently most Rayleigh wave EMT's consisted of single or multiple windings of wire on various forms such as meander-line or grating patterns. Although frequencies up to several megahertz have been achieved by this method, the small-diameter wire required poses problems of difficult fabrication, resistive losses, spurious capacitive effects, poor uniformity, and mechanical fragility.
In contrast to wire-winding methods, excellent uniformity and high resolution can be systematically obtained by conventional photolithography. Thin-film aluminum meander lines deposited on silicon and quartz operating at 15 MHz, however, had large conductor resistance and high insertion losses. Recently, adequate flat conductor thicknesses have been achieved in meander-line EMT's made up to 4.75 MHz by the use of printed circuit board technology. Both the thin film and printing methods, however, require artwork (metallization or etching) skills and facilities.
There currently exists, therefore, a need for a device and method of fabrication that bypasses these requirements. It is desirable that such a device be inexpensive, small, lightweight and capable of conforming to any shape and that the method of fabrication be simple and utilize commercially available components. The present invention is directed toward satisfying such a need.